The present invention relates to a charge pump for transmitting energy and data.
Charge pumps have a wide area of application in electronics for providing a supply voltage. Charge pumps are used when, as well as a first supply voltage, a second supply voltage is also required, the supply voltage range of which lies at least partially outside the first supply voltage or is to be at least partially independent of the first supply voltage. These different supply voltages are referred to as voltage domains.
When operating different voltage domains, energy is supplied to the individual domains by different methods, such as charge pumps or DC/DC converters for example, depending on the energy requirement of a domain.
When charge pumps are used, energy is transmitted from a first domain to a second domain with the help of pump capacitors. Here, the energy-emitting voltage domain is referred to as the primary side and the energy-receiving side as the secondary side.
In many applications, there are different voltage domains between which data have to be exchanged. Different methods are available for this purpose, such as optical transmitters, pulse transmitters or, in the simplest case, level shifters for example. An important aspect in data transmission is the energy required to achieve this. In general, it can be stated that the energy required increases with increasing speed and increasing demands on data integrity.
With charge pumps, methods have been disclosed in which information and data as well as energy can be transmitted from the primary side to the secondary side. They work with the help of a modulation of parameters of the primary side charge pump stage.
With the known methods, a bidirectional data stream cannot be transmitted via the charge pump, as the return path for data from the secondary side to the primary side is missing. With the known methods, a separate data transmission path is required for this reverse transmission.
In addition, the efficiency of the charge pump is reduced due to the modulation, as it is not always possible to work with parameters which are optimum for energy transmission. It is therefore necessary to reach a compromise between energy transmission and data transmission.
It is possible to differentiate between two principles of data transmission depending on the type of data usage: the transmission of an item of data, e.g. a control bit for a function, wherein the item of data is to arrive at a certain point, or is characterized by a certain parameter and does not occur mixed with other data in time or function. This principle of single bit transmission is used where the number of items of data to be transmitted is low or only a very few bits are to be transmitted.
When transmitting a data stream, wherein a plurality of information units are transmitted consecutively in time, it is important to have a time reference in order to be able to assign a relevance in the data stream to each individual information unit, such as a bit or a symbol. This type of transmission is used where quantities of data which cannot be covered by a single bit transmission are transmitted.
Examples of this are serial transmission with the help of a synchronous SPI, an asynchronous RS232 or an LIN interface.
In the case of synchronous transmission, e.g. with an SPI, the length of each bit is determined by a clock pulse transmitted on a second line, enabling the individual bits to be clearly differentiated from one another. In addition, the start and end of a data word, the time-related sequencing of information units, can be signaled by a third line. The relevance accorded to a transmitted information unit is therefore always unambiguous, as its position in the data word can be clearly assigned. As both the length of an information unit and also the start and end of the data word are signaled, it is substantially unnecessary for there to be a relationship between the clock systems of the two domains between which the data are transmitted. That is to say, there is no need for a clock system for demodulating the data on the secondary side.
In contrast with this is the asynchronous RS232 protocol or LIN interface, with which only one information unit is transmitted at a time. The individual units are separated from one another in time so that a clock pulse, which must have a certain stability, must be provided both in the transmitter and in the receiver. For example, a maximum relative deviation between the clock pulses of only 3% is allowed during a data word.
The start and end of the data word are defined by additional information units which are transmitted before and after the data word respectively, e.g. start-of-frame (SOF), stop bits. The advantage of this transmission compared with synchronous transmission lies in the low number of transmission channels required, one, in contrast to two to three transmission channels with synchronous transmission. However, this advantage assumes a stable clock system in the transmitter and the receiver.
One possibility of synchronization between the transmitter and receiver consists in counting the number of periods of the charge pump and thereby determining the length of data symbols. However, this has the disadvantage that a counter with evaluation logic has to be implemented on both sides, wherein the counter with the evaluation logic must be fast enough to count all periods without errors and record the information content correspondingly quickly. In doing so, incorrect or missing count pulses due to interference, e.g. due to transient interference in the transmitter or in the receiver, give rise to shifted counter states when evaluating the charge pump periods which can lead to incorrect interpretation of the data. To prevent this, it is necessary to synchronize the counters or to set them to a predefined value, e.g. 0, sufficiently often.